Urea or carbamide is an organic compound comprising two amine (—NH2) groups joined by a carbonyl (C═O) functional group. It is widely used in fertilizers as a convenient source of nitrogen. However, urea is highly soluble in water which causes the compound to leach into ground or surface water causing low retention in the fertilizer and thereby resulting in reduced fertilizer efficiency. The leaching of urea in surface water causes Eutrophication resulting in a drastic increase in phytoplankton effecting in depletion of oxygen in water and reduction in aquatic life. Further, during summer, urea is lost from the fertilizer due to volatilization where nitrogen is released to atmosphere as ammonia gas. Also, a portion of urea is lost as nitrous oxide due to denitrification under reduced conditions by denitrifying bacteria in the soil. This way up to 60% of the nitrogen in urea is lost to the surrounding causing environmental hazards and a corresponding increase in fertilizer usage.
Several measures have been taken to reduce this loss of urea into the surrounding. Firstly, by applying small amounts of urea to the crop/plant at different growth stages, the nitrogen can be used before being lost. Secondly, by impregnating the urea-based fertilizer deeper into the soil, the loss of nitrogen to the surrounding can be alleviated by retaining the nitrogen in the form of ammonium in the complex of the soil particles. Certain modern technologies use urease inhibitors such as phenylphosphorodieamidate, hydroxamates and benzoqauinones (Gould, W. D. et. al., Adv. Agron. 40: 209-238, 1986). These inhibitors reduce the hydrolysis of urea, thereby reducing loss of ammonia due to volatilization. Further, use of nitrification inhibitors such as N-serve or nitrapyrin (2-chloro-6 (tricholoromethyl)-pyridine), dicyandiamide, 2-amino 4-chloro-6-methylpyrimidine, potassium azide and thiourea has also been suggested to overcome the listed drawbacks. (Sahrawat, Adv. Agron 42: 279-302, 1989; and Prasad and Power, Adv. Agron 54: 233-81, 1995). These compounds although effective are costly and not readily available, which limits their applicability on a large-scale.
Another known method for reducing loss of nitrogen from the fertilizer to the surrounding is by using neem seed cake or neem cake coated urea, where, the naturally occurring neem is found to exhibit nitrification inhibiting properties (Prasad, et. al., Adv. Agron 23: 337-381, 1971). Neem is cheap and readily available in India, therefore favorable for use in India. Neem bittern/extracts such as Nimin and Neemex have been used for incorporation with urea. More recently use of a neem oil urea emulsion adduct is disclosed (Prasad, et. al. Curr. Sci. 75: 15, 1998). Further, Karanjin from Karanj (Pangarnla glabra), tea waste, and medicinal plant product waste like waste of Pyrethrum flower (Crysanthaxium cinerariefolium) have also been reported to retard nitrification (Sahrawat, et. al., Adv. Agron. 42: 279-309, 1989; and Ram, et. al., Indian Soc. Soil Sci. 41: 176-177, 1993). Neem oil/karania oil coated urea enhances the self-life of urea, reduce caking during storage, and increase nitrogen availability to the plants.
The ingredients present in neem seeds/karanja seeds not only act as a natural fertilizer with pesticidal properties but also act as a nitrification inhibitor, which results in slow-release of nitrogen from the fertilizer during the period of crop growth. Also, these ingredients increase the efficiency of the nitrogen-release fertilizer thus considerably decreasing the amount of fertilizer application required and thereby reducing the fertilizer cost. Further, these natural ingredients considerably improve the soil quality and protect the soil during droughts, thus, enhancing the crop yield. Also, since nitrogen does not seep into water bodies, the environmental impact is reduced.
Very often these adapted fertilizers, especially having synthetic chemicals, are limitedly used, on turfs, golf courses, landscapes, parks, or in floriculture, due to their slow-release properties. Because of the expense involved, the application of these fertilizers is not feasible on a large-scale. Several attempts have been made in the past to provide slow-release fertilizers, some of the disclosures are listed in the prior art below.
JP Patent No. 2002080290 discloses an environmentally friendly granular fertilizer which is preserved during storage from insect break-outs by combining at least one material selected from neem organ after the neem oil is extracted, neem oil, and neem grounds with the granulated fertilizer composition also containing at least one material selected from crab shell and shrimp shell.
U.S. Pat. No. 6,315,807 discloses a novel formulation useful as a nitrification and urease inhibitor, said formulation comprises an effective amount of nitrogenous fertilizer, castor oil, and oil derived from Artemisia Annua in an amount sufficient to inhibit the nitrification in the formulation, a method for producing the formulation, and a method for applying the formulation to soil are also disclosed.
U.S. Pat. No. 6,336,949 discloses a novel composition for a slow release nitrogenous fertilizer comprising about 0.5-1% of an inert material and 0.5-1% of essential oil or their derivatives (on weight basis), and a process for manufacturing the composition thereof. To manufacture the composition as disclosed in U.S. Pat. No. 6,336,949 it takes more than 24 hrs.
U.S. Pat. No. 7,722,695 discloses a neem based composition for coating a nitrogenous fertilizer. The method for making the composition comprises mixing neem extract, neem oil, and binders with an organic solvent to obtain the neem based composition which is then coated on urea. A drawback of this method is that since the neem based composition is only superficially adhered to the urea there is a possibility of the coating coming off during storage and transportation of the fertilizer.
The disclosures listed in the prior art generally coat urea by spraying neem oil or applying a neem oil emulsion on the urea surface. The composition is typically provided as prills or beads and packed in hydrophobic polythene bags. During storage and transportation, the oil coated on the urea surface adsorbs on to the hydrophobic surface of the polythene bag, resulting in loss of the neem ingredient and thus degrading the fertilizer quality. The present invention therefore aims at providing a slow-release urea-based fertilizer which overcomes the above-listed drawbacks.